KR20140016190A - Method of manufacturing high aspect ratio silver nanowires - Google Patents

Abstract

A method or manufacturing silver nanowires comprises the steps of: providing a silver ink core component containing 60 wt% or more of silver nanoparticles distributed on a silver carrier; providing a shell component containing film forming polymer distributed on a shell carrier; providing a substrate; forming a core and a shell for surrounding the core by performing the electromagnetic cavity radiation of the silver ink core component and the shell component, and depositing a core shell fiber in which the silver nanoparticles are positioned on the core; and forming nanowires with 60 μm or more of the mean length by processing the substrate with the silver nanoparticles.

Description

Method of Manufacturing High Aspect Ratio Silver Nanowires

The present invention relates generally to the field of silver nanowire manufacturing. In particular, the present invention relates to a method of making long nanowires (preferably ≧ 60 μm) of silver nanowires for use in various applications.

Films that exhibit high conductivity in combination with high transparency are very useful for use as electrodes or coatings in a wide range of electronic applications, including, for example, touch screen displays and photovoltaic cells. Current techniques for these applications include the use of tin doped indium oxide (ITO) containing films deposited via physical vapor deposition. Due to the high capital costs of physical vapor deposition processes, alternative transparent conductive materials and coating treatment methods are being sought. The use of dispersed silver nanowires as the penetrating network is emerging as a promising alternative to ITO containing films. The use of silver nanowires may provide an advantage that can be processed using roll to roll technology. Thus, silver nanowires potentially offer the advantages of high transparency and conductivity and low cost manufacturing over conventional ITO containing films.

A "polyol process" for the production of silver nanostructures has been found. The polyol process uses ethylene glycol (or alternative glycol) as both solvent and reducing agent for the production of silver nanowires. However, the use of glycols has some inherent disadvantages. Specifically, the use of glycol as both a reducing agent and a solvent reduces the control of the excess reaction since the main reducing agent species (glycolaldehyde) are prepared in situ and their presence and concentration depend on the degree of oxygen exposure. In addition, the use of glycols has the potential to form combustible glycol / air mixtures in the space portion of the reactor used to make silver nanowires. Finally, the use of large amounts of glycols incurs associated costs of disposal, increasing the cost of commercialization of these operations.

An example of another alternative polyol process for the production of silver nanowires is disclosed in US Patent Application Publication No. 20100078197 by Miyagishima et al. Miyagishima et al. Comprises adding a solution of a metal complex to a water solvent containing at least a halide and a reducing agent and heating the resulting mixture to a temperature of 150 ° C. or less, wherein the metal nanowires are 50 nm or less in diameter. A method for producing metal nanowires containing metal nanowires having a major axis length of 5 μm has been described.

Nevertheless, there is still a need for alternative methods for the production of silver nanowires, in particular for the production of silver nanowires with long lengths (preferably ≧ 60 μm) without the use of glycols.

The present invention provides a silver ink core component containing ≧ 60 wt% silver nanoparticles dispersed in a silver carrier; Providing a shell component containing the film forming polymer dispersed in the shell carrier; Providing a substrate; Coelectrospinning the silver ink core component and the shell component to deposit core shell fibers on the substrate with the core and the shell surrounding the core and the silver nanoparticles being in the core; It provides a method for producing silver nanowires comprising treating the silver nanoparticles to form a group of silver nanowires having an average length L of ≧ 60 μm.

The present invention provides a silver ink core component containing ≧ 60 wt% silver nanoparticles dispersed in a silver carrier; Providing a shell component containing the film forming polymer dispersed in the shell carrier; Providing a substrate; Co-electrospinning the silver ink core component and the shell component to deposit core shell fibers on the substrate with the core and the shell surrounding the core and the silver nanoparticles being in the core; Treating the silver nanoparticles to form a group of silver nanowires having an average length L of ≧ 60 μm, wherein the silver carrier and the shell carrier have an interfacial tension between the shell component and the silver ink core component at 2 to 5 mN / It provides a method for producing silver nanowires selected to be m.

There is provided a process for producing silver nanowires with an average length L of ≧ 60 μm, avoiding the inherent disadvantages of using glycols.

The term “ high aspect ratio ” as used herein and in the claims with respect to recovered silver nanowires means that the average aspect ratio of the recovered silver nanowires is ≧ 150. Preferably, the recovered silver nanowires have an average aspect ratio ≧ 200. Most preferably, the recovered silver nanowires have an average aspect ratio ≧ 1,000.

Preferably, the silver ink core component used in the silver nanowire manufacturing method of the present invention is ≥ 60 wt% (more preferably ≥ 70 wt%; most preferably ≥ 75 wt%) of silver dispersed in the silver carrier. Nanoparticles.

Preferably, the silver nanoparticles used in the silver ink core component have an aspect ratio of ≦ 2 (more preferably ≦ 1.5; most preferably ≦ 1.1). Silver nanoparticles used optionally include treatments or surface coatings to enable the formation of stable dispersions in silver carriers and to inhibit the formation of aggregates.

The silver carrier used in the silver nanowire manufacturing method of the present invention may be selected from any liquid in which silver nanoparticles can be dispersed. Preferably, the silver carrier is selected from the group consisting of water, alcohols and mixtures thereof. More preferably, the silver carrier is water; C _1-4 alcohols (eg methanol, ethanol, propanol, isopropanol, butanol); Dimethyl sulfoxide; N, N-dimethylformamide; 1-methyl-2-pyrrolidone; Trimethyl phosphate and mixtures thereof. Most preferably, the silver carrier is water.

The silver ink core component used in the silver nanowire manufacturing method of the present invention optionally further includes a core additive. Core additives include surfactants, antioxidants, photoacid generators, thermal acid generators, quenchers, curing agents, dissolution rate modifiers, photocuring agents, photosensitizers, acid amplifying agents, plasticizers, and orientation modifiers. And crosslinkers. Preferred core additives include surfactants and antioxidants.

Preferably, the shell component used in the silver nanowire manufacturing method of the present invention comprises a film forming polymer dispersed in a shell carrier.

The film forming polymer used in the silver nanowire manufacturing method of the present invention may be selected from known electron-radioactive film forming materials. Preferred film forming polymers include polyacrylic acid, polyethylene oxide, polyvinyl alcohol, polyvinyl propylene, cellulose (eg hydroxy propyl cellulose, nitrocellulose), silk and blends thereof. More preferably, the film forming polymer is polyethylene oxide. Most preferably, the film forming polymer is polyethylene oxide having a weight average molecular weight of 10,000 to 1,000,000 g / mol.

The shell carrier used in the silver nanowire manufacturing method of the present invention may be selected from any liquid in which the film forming polymer is dispersible. Preferably, the shell carrier may be any solvent in which the film forming polymer is well soluble. More preferably, the shell carrier has an interfacial tension between the shell component and the silver ink core component> 0.1 mN / m (preferably> 1 mN / m; more preferably> 2 mN / m; most preferably Is chosen to be 2 to 5 mN / m). When used in combination with a silver ink core component containing water as the silver carrier, the shell carrier is preferably selected from the group consisting of water alcohol mixtures; Wherein the alcohol is selected from the group consisting of acetone, C _1-4 alcohols (eg methanol, ethanol, isopropanol, propanol, butanol, tert-butanol) and mixtures thereof; The water alcohol mixture exhibits an alcohol concentration of ≧ 50 wt% (more preferably> 50 wt%).

The shell component used in the silver nanowire manufacturing method of the present invention optionally further includes a shell additive. The shell additive may be selected from the group consisting of surfactants, antioxidants, photoacid generators, thermal acid generators, quenchers, curing agents, dissolution rate modifiers, photocuring agents, photosensitizers, acid amplifying agents, plasticizers, orientation modifiers and crosslinking agents. Preferred shell additives include surfactants and antioxidants.

Particularly preferred shell components used in the silver nanowire manufacturing method of the present invention are 1 to 25 wt% (more preferably 1 to 15 wt%; most preferably, a film forming polymer dispersed in a water and C _1-4 alcohol mixture shell carrier). Preferably 2 to 10 wt%). Preferably, the shell carrier is a mixture of water and C _1-4 alcohol having an alcohol concentration of ≧ 50 wt% (most preferably ≧ 60 wt% alcohol). Most preferably, the shell component comprises 2 to 10 wt% polyethylene oxide in the shell carrier, wherein the shell carrier is a water ethanol mixture with an ethanol content ≧ 50 wt%.

The substrate used in the silver nanowire manufacturing method of the present invention may be selected from any known substrate, both conductive and nonconductive. Preferred substrates include glass (eg Willow ^® glass available from Corning, Inc.), plastic films (eg polyethylene, polyethylene terephthalate, polycarbonate, poly methyl methacrylate), metals (eg For example, aluminum, copper), conductive treated paper, conductive nonwoven fabric, conductive liquid bath (eg, water, water electrolyte mixture). Preferably, the substrate used in the silver nanowire manufacturing method of the present invention is later selected to be embedded in a device (eg, as part of a transparent conductor assembly in a touch screen device). Preferably, the substrate used in the silver nanowire manufacturing method of the present invention is selected to enable subsequent processing of silver nanowires deposited thereon (e.g., recovery / separation of nanowires from the substrate).

Preferably, the process for producing the silver nanowires of the present invention comprises silver ≧ 60 wt% (more preferably ≧ 70 wt%; most preferably ≧ 75 wt%) of the silver nanoparticles dispersed in the silver carrier. Providing an ink core component; Providing a shell component containing the film forming polymer dispersed in the shell carrier; Providing a substrate; Coelectrospinning the silver ink core component and the shell component to deposit core shell fibers having a core and a shell surrounding the core on the substrate and the silver nanoparticles being in the core; Treating the silver nanoparticles to form a group of silver nanowires having an average length L of ≧ 60 μm (preferably 60 to 10,000 μm; more preferably 100 to 10,000 μm; most preferably 500 to 10,000 μm) do.

Preferably, the process for producing the silver nanowires of the present invention comprises silver ≧ 60 wt% (more preferably ≧ 70 wt%; most preferably ≧ 75 wt%) of the silver nanoparticles dispersed in the silver carrier. Providing an ink core component; Providing a shell component containing the film forming polymer dispersed in the shell carrier; Providing a substrate; Coelectrospinning the silver ink core component and the shell component to deposit core shell fibers having a core and a shell surrounding the core on the substrate and the silver nanoparticles being in the core; The silver nanoparticles are treated to have an average diameter D of ≦ 5 μm (preferably between 100 nm and 5 μm; more preferably 1 to 5 μm) and an average length L of ≧ 60 μm (preferably between 60 and 10,000 μm; more Preferably from 100 to 10,000 μm; most preferably from 500 to 10,000 μm (preferably here the aspect ratio L / D of the silver nanowires is ≧ 150 (more preferably ≧ 200; even more preferably ≧ 500; most preferred Preferably ≧ 1,000).

Preferably, in the method for producing silver nanowires of the present invention, the core shell fibers are deposited on the substrate in a redundant pattern selected from the group consisting of random overlapping patterns and controlled overlapping patterns, wherein the silver nanowire group is conductive Form a network. Preferably, the formed conductive network has a sheet resistance R _s of <100 Ω / sq.

In the method for producing silver nanowires of the present invention, the silver nanoparticles in the core shell fibers deposited on the substrate may be sintered (eg, photosintered, thermally sintered); Selected from the group consisting of heating (e.g., burn-off, micro pulse photonic heating, continuous photonic heating, microwave heating, oven heating, furnace heating) and combinations thereof Is handled using technology. Preferably, the silver nanoparticles in the core shell fibers deposited on the substrate are treated with photosintering.

Preferably, in the method for producing silver nanowires of the present invention, co-electrospinning includes supplying a silver ink core component and a shell component through a common annular nozzle having a central opening and a peripheral annular opening, wherein the silver ink The core component is supplied through the central opening and the shell component is supplied through the peripheral annular opening. Preferably, the cross-sectional area CSA _annular shell material volume flow rate, volume flow rate, the ratio of the VFR _core has a peripheral vertical to the flow direction of the annular opening of the core material to be fed through the VFR _shell-center opening of which is supplied via a peripheral annular opening for It is greater than or equal to the ratio of the cross-sectional area of the central opening perpendicular to the flow direction. More preferably, the following expressions are satisfied by the process conditions:

Most preferably, the following expressions are satisfied by the process conditions:

Preferably, in the method for producing silver nanowires of the present invention, the silver ink core component is 0.1 to 3 μL / min (preferably 0.1 to 1 μL / min; more preferably 0.1 to 0.7 μL / min; most preferred Preferably through a central opening at a volume flow rate of 0.4 to 0.6 μL / min.

Preferably, in the method for producing silver nanowires of the present invention, the shell component is 1 to 30 μL / min (preferably 1 to 10 μL / min; more preferably 1 to 7 μL / min; most preferably Feed through the peripheral annular opening at a flow rate of 4-6 μL / min).

Preferably, in the method of making silver nanowires of the present invention, the common annular nozzle is fixed with a positive applied potential difference with respect to the substrate. More preferably, the applied potential difference is between 5 and 50 kV (preferably between 5 and 30 kV; more preferably between 5 and 25 kV; most preferably between 5 and 10 kV).

Some embodiments of the invention will now be described in detail in the following examples.

A dual nozzle electrospinator model EC-DIG, from IME Technologies, was used to electrospin silver nanowires in the examples. The nozzles used in the examples include an outer opening 0.6 mm in inner diameter and 1.2 mm in outer diameter and having an annular cross section perpendicular to the material flow direction and concentric with the inner opening; And a coaxial nozzle (EM-CAX from IMM Technologies) with an internal opening with a circular cross section of 0.4 mm in diameter perpendicular to the material flow direction. During material spinning, the silver ink core component is supplied through the inner opening of the coaxial nozzle and the shell component is supplied through the outer opening of the coaxial nozzle. The silver ink core component and the shell component are independent syringe pumps that control the volume flow rate of the silver ink core component, the VFR _core at 0.5 μL / min, the shell flow volume, and the VFR _shell at 5 μL / min (EP manufactured by EP Technologies, Inc.). -NE1) to feed through the coaxial nozzle. In the examples the electrospinning process was performed at ambient conditions in a laboratory controlled at 20 ° C. and 25-35% relative humidity.

The substrate used for the fiber collection in the examples was a glass slide with a diameter of 60 mm and a thickness of 0.16-0.19 mm. During the spinning operation, the spinning head was placed vertically on the substrate and the glass plate was placed on top of the ground electrode. During spinning, a positive potential was applied to the spinning head. The voltage used in the examples was lowered to 9 kV at 9 kV at the onset of radiation and once the spinning process stabilized.

Photonic sintering mentioned in the examples was performed using a Pulseforge 3100 photon generator available from Novacentrix. Photon generators are equipped with high-intensity xenon lamps that can emit a broad spectrum from UV to short IR. The photon generator was set at 350 V for 400 μsec pulse generation at 5 Hz frequency in a continuous mode generating 2.46 J / cm ² . The sample was fed through a photon generator on the conveyor belt at a speed of 7.62 m / min.

Reported sheet resistance values for the photonic sintered samples were measured according to ASTM F390-11 using a Jendel HM-20 colliner four point probe test unit from Janel Engineering Limited.

Percent transmission versus wavelength measurements reported in the examples were performed using an HP lambda 9 UV VIS spectrometer.

Example 1-2 Preparation of Silver Nanowires by Coaxial Electrospinning

Silver nanowires were electrospun in Examples 1 and 2, respectively, and deposited on glass slide substrates. The silver ink core components used in Examples 1-2 consisted of 75 wt% silver nanoparticles (available as CSD-95 from Cabot Corporation) with a nominal particle size of 50 nm dispersed in water. The shell component used in Examples 1-2 consisted of 6 wt% polyethylene oxide (400,000 g / mol available from Aldrich) dissolved in 40/60 wt% water / ethanol solution, where The interfacial tension between the silver ink core component and the shell component was measured to be 2-5 mN / m.

The sheet resistance of the silver nanowire networks deposited from Examples 1 and 2 measured before and after photonic sintering is shown in Table 1.

Example The product silver nanowire network after sintering from 1 was analyzed by optical microscopy and found to be silver nanowires with diameters ranging from 1 to 5 μm and lengths ranging from 800 to 1,000 μm.

Example After sintering from 1 the product silver nanowire network was analyzed spectrometer and found that the percent transmission was ≥ 70% over the visible spectrum of 390 nm to 750 nm.

Example
number Photonic Sintering
(kΩ / sq) After Photonic Sintering
(Ω / sq) One 360.4 ± 36.8 44.6 ± 4.6 2 431.5 ± 30.9 57.4 ± 2.1

Comparative Example A1

The silver ink core component used in Comparative Example A1 consisted of 60 wt% silver nanoparticles (available as PFI-722 ink from PChem Associates, Inc.) dispersed in water. Various shell components were used in Comparative Example A1, including:

6 wt% polyacrylic acid in water;

4 wt% polyethylene oxide in 60/40 wt% ethanol / water mixture;

6 wt% polyethylene oxide in 60/40 wt% isopropanol / water mixture;

8 wt% polyacrylic acid in 30/20/50 wt% water / isopropanol / butanol mixtures;

4-6 wt% polyethylene oxide in 60/40 wt% ethanol / water mixture;

4-8 wt% polyacrylic acid in 60/40 wt% ethanol / water mixture; And

4-8 wt% polyacrylic acid in 40/60 wt% ethanol / water mixture.

The interface tension between the silver ink core component and the shell component in each of these systems was determined to be 0.4-2 mN / m.

Efforts to produce silver nanowires by combining the silver ink core components with the described shell components have not been successful.

Comparative Example A2

The silver ink core component used in Comparative Example A2 consisted of 60 wt% silver nanoparticles (available as PFI-722 ink from Pchem Chem Associates) dispersed in water. Various shell components were used in Comparative Example A2, including:

6 wt% polyacrylic acid in water;

4 wt% polyethylene oxide in 60/40 wt% ethanol / water mixture;

6 wt% polyethylene oxide in 60/40 wt% isopropanol / water mixture;

8 wt% polyacrylic acid in 30/20/50 wt% water / isopropanol / butanol mixtures;

4-6 wt% polyethylene oxide in 60/40 wt% ethanol / water mixture;

4-8 wt% polyacrylic acid in 60/40 wt% ethanol / water mixture; And

4-8 wt% polyacrylic acid in 40/60 wt% ethanol / water mixture.

The interface tension between the silver ink core component and the shell component in each of these systems was determined to be 0.4-2 mN / m.

The silver ink core component is individually combined with each of the described shell components to form a co-electrospinning process (the above embodiment. Efforts to make silver nanowires (as described and used in 1) have not all succeeded.

Claims (10)

Providing a silver ink core component containing ≧ 60 wt% silver nanoparticles dispersed in a silver carrier;
Providing a shell component containing the film forming polymer dispersed in the shell carrier;
Providing a substrate;
Co-electrospinning the silver ink core component and the shell component to deposit core shell fibers on the substrate with the core and the shell surrounding the core and the silver nanoparticles being in the core;
Treating the silver nanoparticles to form a group of silver nanowires having an average length L of ≧ 60 μm,
Method for producing silver nanowires. The method of claim 1, wherein the silver carrier and the shell carrier are selected such that the interfacial tension between the shell component and the silver ink core component is between 2 and 5 mN / m. The method of claim 2, wherein the core shell fibers are deposited on the substrate in an overlapping pattern selected from the group consisting of a random overlapping pattern and a controlled overlapping pattern, wherein the silver nanowire group forms a conductive network. The method of claim 2 wherein the silver nanoparticles are treated with photosintering. 3. The method of claim 2, wherein the co-electrospinning comprises supplying a silver ink core component and a shell component through a common annular nozzle having a central opening and a peripheral annular opening, wherein the silver ink core component is supplied through the central opening and , The shell component is supplied through the peripheral annular opening. The method of claim 2 wherein the aspect ratio (L / D) of the silver nanoparticles is ≦ 2. 3. The silver carrier of claim 2 wherein the silver carrier is water. The shell carrier is a water alcohol mixture, wherein the water alcohol mixture comprises ≧ 50 wt% alcohol. The method of claim 5, wherein the silver ink core component is supplied through the central opening at a flow rate of 0.1 to 3 μL / min and the shell component is supplied through the peripheral annular opening at a flow rate of 1 to 30 μL / min. 6. The method of claim 5 wherein the nozzle is fixed with a positive applied potential difference relative to the substrate. 10. The method of claim 9, wherein the applied potential difference is between 5 and 50 kV.